The present invention generally relates to wireless communication systems, and particularly relates to controlling the power of the Reverse Power Control channel in a high data rate packet network.
Transmit power control factors prominently in a number of wireless communication schemes. For example, conventional Code Division Multiple Access (CDMA) systems, such as those defined by the IS-95B standard, use both reverse link and forward link power control. Generally, these schemes use the receiving end to provide power control feedback information. Thus, for forward link power control in a conventional CDMA network, a handset or other type of access terminal provides power control information to the network transmitter, indicating whether the transmitter should increase or decrease its transmitted power to the terminal.
The above power control schemes are closed loop, meaning that transmit power is controlled based on actual receiver conditions. Characteristically, closed loop power control relies on dedicated power control channels or sub-channels. For example, in conventional CDMA systems, forward link power control relies on power control bits provided by terminals on their reverse link power control channels.
As communication systems evolve, offering greater system capacity, higher data rates, and new applications, the channel structures used to carry data traffic and control information between communication networks and access terminals have become increasingly sophisticated. For example, in the TIA/EIA/IS-856 standard covering high data rate (HDR) packet data networks, the forward link channel structure intermixes both code and time multiplexed channels. HDR networks configured in accordance with the TIA/EIA/IS-856 standard are also referred to as “1x EVDO” networks, indicating the first stage of evolutional advancement beyond the TIA/EIA/IS-2000 standard toward third-generation CDMA networks for data-only applications.
In HDR networks, the forward link traffic channel from a network transmitter to an access terminal is rate controlled rather than power controlled. That is, a HDR network transmitter always transmits at maximum power on its forward link traffic channels, with each access terminal served by the transmitter requesting the maximum data rate that the available power will support. In general, a terminal closer to the transmitter receives data at a higher rate than one further away, but more broadly one might state that terminals request higher data rates from the network as reception conditions improve at the terminal. The TIA/EIA/IS-856 standard defines sixteen data rates at which terminals may request to receive forward link traffic channel data.
Other forward link channels used in HDR networks are not rate controlled. For example, the Reverse Power Control (RPC) channel is a forward link channel transmitted to access terminals at a constant data rate. Access terminals use information received from the network on the RPC channel to control their reverse link transmit power. Thus, the RPC channel is used by the network to implement closed loop control of access terminal transmit power to minimize interference between terminals.
However, there exists no explicit mechanism for controlling the power of the forward link RPC channel. Defining a reverse link channel or sub-channel on which RPC channel power control information might be carried would be inefficient and in any case is not provided for in the standard. Nonetheless, controlling RPC channel power on the forward link based on actual reception conditions at the access terminals would be advantageous.